Reading it, it seems like Irresistible would ONLY be good in MPDC & dungeon. It would mostly be a detriment in PVP...

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For Dungeon I think most people go automatic unless you are really new to the game and the dungeon team is weak. For MPDC most will have their preferred setup to start with, essentially anything that can kill pig quickly or control the boss (Dr P).

So far is seems not. People are also saying she is bugged at the moment.
But I guess it depends on what 5* yellow birds you have & if you think need one soon...
After back to back yellow bird events I suspect it will be awhile before we see another one. But with Rovio's bizarre mind set lately who knows?